This invention relates to gear ball joints and particularly to gear ball joints utilized in driving mechanisms for progressing cavity pumps. Such pumps comprise a partially elastic stator having a helical cavity and a helical rotor having one less helical turn than the stator. For general background information regarding the design of such pumps reference may be made to Moineau U.S. Pat. No. 2,028,407.
Modern versions of such pumps are oftentimes driven by suitable driving means connected to the rotor by a pair of gear ball joints as generally illustrated in FIG. 1 of the appended drawing. Such gear ball joints are particularly well adapted to cope with the complex rotary motion of the end of the rotor. As illustrated in FIG. 1, a progressing cavity pump 10 may comprise a stator 11 and a rotor 12 and suitable inlet means 13 for providing a viscous fluid to the pumping cavity. Rotary driving motion is transmitted to rotor 12 by a first gear ball joint 14 driven by a connecting rod 16 and a second gear ball joint 15.
In progressing cavity pumps of the type illustrated in FIG. 1 it is necessary to provide fluid seals for gear ball joints 14 and 15. Sealing devices applied to such use are subject to considerable wear and are prone to failure from time to time. Typical prior art sealing means as applied to second gear ball joint 15 are illustrated in FIGS. 2 and 2A of the drawings.
As illustrated in FIG. 2 a prior art gear ball joint comprises a gear ball 21 driven by a ring gear 22 and supported on a connecting rod 26 by a primary thrust plate 23 and a secondary thrust plate 24. The ring gear 22 is keyed to a drive shaft 99. Drive shaft 99 drives the ring gear 22 and also a shaft connector 25, which in turn drives an annular shaft 32 surrounding connecting rod 26. During normal use of the pump a working fluid (not illustrated) fills the space within annular shaft 34. This fluid is prevented from seeping into the gear ball joint by means of a seal 27 seated on connecting rod 26 between a retainer 28 and a seal support 29. Connecting rod 26 is provided with a surface groove 30 for receiving a mating projection on seal 27.
As illustrated in FIG. 2A the prior art seal 27 comprises a flexible seal member 31 bonded to a metal washer 32. Washer 32 is provided for the purpose of supporting the seal member 31 during the assembly process. This design has a problem in that it has metal-to-metal sealing surfaces and is susceptible to failure of the rubber-to-metal bond. Furthermore, the exterior portion of the seal has only a single rather limited sealing surface as designated by the reference numeral 33. This seal is prone to leakage during use, so that the pump must be disassembled from time to time for seal replacement.
It is therefore seen that there is a need for a seal for a gear ball joint having improved sealing properties and extended life. PG,4